class User {
    constructor({ username, email }) {
      this.username = username;
      this.email = email;
      // 可以添加其他属性...
    }
  
    save(callback) {
      // 假设这里是将用户保存到数据库的操作，这里只是模拟
      const savedUser = { id: 2, username: this.username, email: this.email };
      callback(null, savedUser);
    }
  }
  
  module.exports = User;
  